Concurrent comparison of epidemiology, clinical presentation and outcome between adult patients suffering from the pandemic influenza A (H1N1) 2009 virus and the seasonal influenza A virus infection

Purpose of studyThe demographics, clinical features and outcome of patients with pandemic influenza A (H1N1) 2009 infection were compared with a concurrent cohort of patients with seasonal influenza A infection.Study designThe clinical and microbiological data of hospitalised adult patients admitted between 29 June and 28 October 2009, with pandemic A (H1N1) 2009 or seasonal influenza A infection, were analysed.ResultsA total of 186 patients including 69 pandemic A (H1N1) and 117 seasonal influenza were analysed. The majority (75%) under 50 years of age had pandemic A (H1N1). Compared with seasonal influenza, pandemic A (H1N1) patients were younger (median age 47 years vs 76 years, p